President Barack Obama gave vent last week to an uncharacteristic show of emotion over the barbaric beheading of American journalist James Foley by the militant jihadi group the Islamic State. He denounced the group as a "cancer" in the region and accused it of rampaging "across cities and villages, killing unarmed civilians in cowardly acts of violence" as it seized a third of Syria and Iraq.

Yet for months, as this cancer metastasized, the White House refused to recognize the growing Islamic State danger — despite warnings from the State Department and the intelligence community. In January, Obama famously dismissed the group as a local "JV team" trying to imitate al-Qaida, but with no capacity to threaten us.

Only recently, when his hand was forced, did the president act — after the Islamic State had taken Iraq's largest city, Mosul, marched toward Baghdad, and threatened the Kurdish city of Erbil — and was poised to slaughter 70,000 members of the minority Yazidi sect. U.S. air strikes have helped the Kurds push the group back and retake Iraq's most important dam, as well as to rescue most of the Yazidis.

But the president still hasn't laid out a coherent strategy to deal with a group that is now more dangerous than al-Qaida. How can he, when his administration is still downplaying the threat? The White House motto appears to be "think small and insist the Islamic State is mostly an Iraqi problem."

Thus, the president's rationale for the air strikes was the need to protect U.S. personnel in Erbil and in Baghdad, and to prevent a humanitarian catastrophe for the Yazidis. He justified the strikes to help recapture the Mosul dam as needed because, had Islamic State fighters breached the dam, it could have flooded our massive embassy in Baghdad. Pretty tortured logic given that the dam is more than 270 miles away.

When asked on Aug. 9 about the threat, deputy national security adviser Tony Blinken insisted in a TV interview that the group presented no immediate threat to the United States.

"Unlike core al-Qaida," Blinken said, "right now, their focus is not on attacking the U.S. homeland or attacking our interests here in the United States or abroad. It's focused intently on trying to create a caliphate now in Iraq and a base from which over time to operate."

Yet that assessment has been repeatedly contradicted by the administration's own experts. The Islamic State "is al-Qaida in its doctrine, ambition, and, increasingly, in its threat to U.S. interests," said Brett McGurk, the deputy assistant secretary of state for Iraq, at a recent House Foreign Affairs Committee hearing. "In fact, it is worse than al-Qaida."

McGurk said the group had become so strong — after seizing enormous quantities of U.S.-made heavy weapons when it took Mosul — that it was "no longer a terrorist organization. It is a full-blown army." The group has amassed hundreds of millions of dollars from extortion, from robbing banks, and from selling oil from wells and refineries it has seized in Syria.

McGurk added that the Islamic State leader, Abu Bakr al-Baghdadi, "seeks to follow in the footsteps of Osama bin Laden as the leader of a global jihad, but with further reach — from his own terrorist state in the heart of the Middle East."

After bin Laden was killed in May 2011, Baghdadi eulogized him and promised "violent retaliation." His audio messages routinely contain thinly veiled threats against the United States, and he has promised in a "message to the Americans" that "we will be in direct confrontation."

Islamic State suicide bombers in Iraq, says McGurk, who average 30 to 50 bombs per month, are increasingly Western passport holders. The group "boasted that an Australian and a German blew themselves up in Baghdad," said the diplomat, "and it is a matter of time before these suicide bombers are directed elsewhere."

Indeed, FBI Director James Comey, Director of National Intelligence James Clapper, Homeland Security Secretary Jeh Johnson, and Attorney General Eric Holder have all expressed concerns about the threat posed by thousands of European jihadis and dozens of Americans, trained by the Islamic State, who could return home undetected.

In other words, the threat is far bigger than the possibility that some U.S. embassy employees would get their feet wet.

We all understand that Obama doesn't want to get sucked back into a counterterrorism war in the country from which he withdrew the last American troops. (Never mind that no one, repeat, no one — not even Sen. John McCain — wants U.S. ground troops to return to battle in Baghdad or Mosul or Anbar.)

We know that Obama hopes Iraq's Shiite leaders will somehow rise to the challenge and woo back alienated Sunnis, thus undercutting the Islamic State. Whether or not that happens, denying the threat the group presents to the United States only delays the development of an adequate U.S. strategy.

At a minimum, that strategy would involve U.S. arming and continuing air support of the reliable Iraqi Kurds; giving better intelligence and possible air support to Baghdad; figuring out how to degrade Islamic State training camps in Syria; and organizing Iraq's Sunni allies into a coherent anti-Islamic State stand.

None of that can happen so long as the White House insists on downplaying the nature of the group. It's time for Obama to tell the U.S. public the truth about the Islamic State threat.

Trudy Rubin is a columnist and editorial-board member for the Philadelphia Inquirer. Email at trubin@phillynews.com.